The present invention relates to a coated fabric excellent in friction characteristics and tear strength. The present invention relates, in more detail, to a coated fabric, used for producing lightweight airbags excellent in deployability and stowability, and an airbag.
Equipping an automobile with airbag as occupant-protecting safety systems, has become standard. An airbag as an occupant-protecting safety system is usually mounted, in a defined site such as a steering wheel or an instrument panel, as a module including an inflator case. Therefore, the storage volume of an airbag is required to be small (compact). In order to produce an airbag with a small storage volume, a woven fabric prepared from a fine yarn is used as a base fabric, and the type and coating amount of an elastomer used for coating are adjusted. For example, the size of the weaving yarn of the base woven fabric has been reduced from 940 dtex to as small as 470 dtex. Moreover, the type of elastomer has been changed from chloroprene to silicone, and the coating amount has been changed from 90 to 120 g/m2 to 40 to 60 g/m2. Recent requirements for an airbag that has been made lightweight and compact are as follows: to make the base fabric more lightweight; to make the hand touch of the base fabric softer; and to make the coated fabric lightweight by decreasing the coating amount of the elastomer. In order to satisfy the requirements, it is indispensable to solve the following technical problems explained below. One of the problems relates to a reduction in the coating amount of a silicone resin composition, and the following two problems arise: (1) a problem of ensuring air-impermeability; and (2) a problem of flame proofness and ensuring the qualification of burning speed defined by FMVSS 302. Another problem is associated with the problem of making an airbag soft. This problem relates to an improvement in the deployability of a lightweight airbag which can be compactly stowed in the airbag module. When an occupant is properly seated at a standard predetermined seating position, and the distance between the occupant and the airbag is small, namely, even when the delayed occupant restraint time is short, the airbag is required to be able to restrain the occupant by rapidly and completely deploying within several tens of milliseconds (msec). Thus, the problem of softening an airbag relates to an improvement in the airbag which improvement makes it have the following highly excellent properties; the airbag in a more compactly stored state smoothly deploys in a short period of time.
As disclosed in Japanese Unexamined Patent Publication (Kokai) No. 6-8779, the coated film of elastomer on a fabric for the conventional airbag is predominantly applied to meshed openings of a woven fabric. When the coating amount of an elastomer is 25 g/m2 or less, on the base woven fabric, the coated elastomer on yarn portions other than the mesh openings of the fabric is decreased, and the spaces between single filaments in the weaving yarn portions are not completely covered. As a result, a base fabric having predetermined air-shielding properties cannot be obtained. Since an airbag must basically function so that the airbag deploys in a short period of time to restrain an occupant, the airbag is desirably formed from a gas impermeable fabric that can completely utilize the gas generated by an inflator. Moreover, for a fabric structure prepared by unevenly coating a fabric with an elastomer, portions of the applied coating where the thickness is small are broken during a burning test by FMVSS 302 reguration, and diffusion of the burning gas cannot be suppressed. As a result, a coated fabric that will be rejected after a FMVSS 302 burning test is formed.
Japanese Unexamined Patent Publication (Kokai) No. 7-300774 discloses a coated fabric for airbags that has a 5 to 20 xcexcm thick coated film of a pigment-containing silicone resin composition containing from 5 to 10% by weight of a pigment and that passes a FMVSS 302 burning test. However, because the coated fabric is prepared in a method wherein the coated film is formed in a gap between the woven base fabric surface and the knife of a coating head, and the coated film has a thickness approximately equal to the gap, it is understood that the surface of the 5 to 20 xcexcm thick coated film, formed after filling recesses and protrusions on the woven fabric surface, forms a flat, even surface. The coated fabric naturally shows a high frictional fabric face due to the flat, smooth coated film surface.
International Patent Publication WO 01-09416 discloses an airbag formed from a self-extinguishing, uncoated fabric in which a high density woven fabric composed of a fine yarn (a yarn size of 250 dtex or less, and a single filament size of 4.5 dtex or less) is used as a base fabric, and particularly discloses a base fabric which is prepared by applying a lubricant to an unscoured woven fabric and from which a small, lightweight, compact airbag can be obtained.
However, for a conventional light weight airbag that can be folded in a small size and compactly stowed in the airbag module, no specific attempt has been known to design a coated fabric capable of providing an air bag with an improved all-out performance covering deployability enabling air bag to deploy with a shorted period of time, resistance to inflating pressure at deployment air impermeability and flame proofness.
Furthermore, an object of the present invention is to realize a lightweight airbag that can satisfy the requirements that the airbag shows a short deployment time, an excellent deployment uniformity and the ability to rapidly restrain an occupant, that is excellent in deployment pressure resistance and that can be compactly stowed in the casing of an airbag system.
A more specific object of the present invention is to provide a lightweight coated fabric that is flexible although it has a gas impermeable elastomer coating and that shows improved friction characteristics and tear strength. A further object of the present invention is to provide a lightweight coated fabric that shows an air-shielding ability advantageous to airbag deployment even when the coating amount of the elastomer coating is small, and that passes flame proofness and burning speed tests defined by FMVSS 302.